while sighax itself is unpachable, everybody should keep in mind, that its still possible to remove it from The system, if nintendo finds ways to workaround the firmprotection, or if a cfw is used that doesn't have firm protection.
This on the other side sighax is not that different from arm9loaderhax, the only advantages are:
a bit earlier in boot -> access to the console unique otp without downgrade, which could have advantages in future, while its not needed anymore after the firsr sighax release
only one firm partition is needed -> maybe the backup partition could be used as sighax backup
no need to modify the key store -> no bricks on unprotected updates on the new 3ds
Also a good recovery strategy to help to save the 3ds in most situations would be sighax+injected dsi ware exploid game+save.
This way you would be able to fix the most briks using sighax, and also be able to restore sighax, if it gets somehow overwritten using the dsi exploid